The Sylph are significantly more powerful than originally thought..
Spell Power is listed at 15 so they are effectively powered at 60.
Other than the healing property that avoids the Undead check+penalty... there is one other property worth pointing out.
Part of the magic damage algo factors in magic defense... but it cuts the magic defense by a factor of 2!
Yes, I tried to use this summon vs higher magic defense targets... and other than those that have the maximum magic
defense to start with (254),
the spell really cuts though the Ging-Ryu (Yellow Dragon in FF4A) and Blue Dragon.